bcachefs: Move BCACHEFS_STATFS_MAGIC value to UAPI magic.h

Move BCACHEFS_STATFS_MAGIC value to UAPI <linux/magic.h> under
BCACHEFS_SUPER_MAGIC definition (use common approach for name) and reuse the
definition in bcachefs_format.h BCACHEFS_STATFS_MAGIC.

There are other bcachefs magic definitions: BCACHE_MAGIC, BCHFS_MAGIC,
which use UUID_INIT() and are used only in libbcachefs. Therefore move
only BCACHEFS_STATFS_MAGIC value, which can be used outside of
libbcachefs for f_type field in struct statfs in statfs() or fstatfs().
Suggested-by: Su Yue <glass.su@suse.com>
Signed-off-by: Petr Vorel <pvorel@suse.cz>
Acked-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bcachefs_format.h

@@ -76,6 +76,7 @@
 #include <asm/byteorder.h>
 #include <linux/kernel.h>
 #include <linux/uuid.h>
+#include <uapi/linux/magic.h>
 #include "vstructs.h"
 
 #ifdef __KERNEL__
@@ -1290,7 +1291,7 @@ enum bch_compression_opts {
 	UUID_INIT(0xc68573f6, 0x66ce, 0x90a9,				\
 		  0xd9, 0x6a, 0x60, 0xcf, 0x80, 0x3d, 0xf7, 0xef)
 
-#define BCACHEFS_STATFS_MAGIC		0xca451a4e
+#define BCACHEFS_STATFS_MAGIC		BCACHEFS_SUPER_MAGIC
 
 #define JSET_MAGIC		__cpu_to_le64(0x245235c1a3625032ULL)
 #define BSET_MAGIC		__cpu_to_le64(0x90135c78b99e07f5ULL)

include/uapi/linux/magic.h

@@ -37,6 +37,7 @@
 #define HOSTFS_SUPER_MAGIC	0x00c0ffee
 #define OVERLAYFS_SUPER_MAGIC	0x794c7630
 #define FUSE_SUPER_MAGIC	0x65735546
+#define BCACHEFS_SUPER_MAGIC	0xca451a4e
 
 #define MINIX_SUPER_MAGIC	0x137F		/* minix v1 fs, 14 char names */
 #define MINIX_SUPER_MAGIC2	0x138F		/* minix v1 fs, 30 char names */